Amplifier



VN. c. NORMAN AMPLIFIER Filed sept. 2e, 195e /NVEA/Ton N. C .N ORM/4N By ATTORNEY AMAA April 11, 1939.

Patented Apr. 11, 1939 UNiTED STATES PATENT oFFicE AMPLIFIER,

Nathaniel C. Norman, New York, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application September 26, 1936, Serial No. 102,703 3 Claims. (Cl. 179-171) This invention relates to amplifiers and parated from the alternating current supply 'l in ticularly to amplifiers for use with cathode ray the usual way. Some of the electrons emitted tube apparatus, such as Oscilloscopes. by the cathode 3 are drawn through anodes 5 For some applications of such apparatus the and 8 and pass between the two sets of deflectsignal currents to be amplified are derived from ing plates 9, 9 and I 0, I 0 to the screen II at ik unsyinmetrically grounded or unbalanced sources the end of the tube. In accordance with the such as a simple microphone. In other cases usual procedure the voltages representing the they are derived from a symmetrically grounded phenomena to be observed are impressed on the or balanced source, such as a push-pull microplates I0, II) and a sweep voltage synchronized 10 phone and in still other cases the current to be with the phenomena is impressed on the plates 10 amplied may be continuous. 9, 9, to provide the time axis. Since the ampli- The object of this invention is an improved fiers I2 and I3 associated with the two sets of amplier which is particularly well adapted for plates are identical only one of them will be deuse with cathode ray tube apparatus. scribed in detail.

` An amplifier according to this invention com- The amplifier I2 comprises two vacuum tubes l5 prises two vacuum tubes with both their input I4 and I5 which are energized by a conventional and output circuits connected by resistor elements rectifier I6. In order to avoid unnecessary in push-pull relation. A feedback path is procomplication of the drawing the filament circuits vided between the output circuit of one tube have not been shown but it will be understood and the input circuit of the other whereby unthat they maybe energized from the winding 44 20 balanced signals impressed on the rst tube are on the transformer 45 supplying the rectifier I6. converted into balanced signals in the output cir- With the potentiometer I1 in its extreme clockcuit. When balanced signals are impressed wise position contact I8 is held open by the arm across both input circuits the feedback path is I9 and the input circuits of the tubes @Omprsopened and the amplifier then functions as a ing the COllDlng potentimeter I7 and leSiStOl 25 conventional push-pull amplifier. The input re- 2U, the COI1tr01 grids 2| 22, Cathodes 23, 24 and sistor element of the rst tube is preferably a the potentiometers 25, 26 are connected in balpotentiometer associated with the switch in the anced push-pull relatOn as ShOWn. The 01113D1115 feedback path in such a way as to open the circuits comprising the tube cathodes 23, 24, the

,o path when the potentiometer is adjusted to the potentiometers 25, 26. the resistors 21, 28, 29 30 position of balanced input circuits. and 30 and the tube plates 3|. 32, which are When such an amplifier is used t0 apply p0- directly connected to the deflecting plates I0, I0

tentials to the plates of a cathode ray tube, it of the cathode ray tube, are also connected in n is often necessary to vary the relative outputs of push-pull relation and are Supplied With plate the two tubes to vary the position of the electron potential over the conductor 41 by the rectifier B- 35 beam but as these tubes usually operate at high The arms 33, 34 0f the potentiometers 25, 26 plate potentials, it is very desirable to avoid the are shown for convenience as mounted on sepause of the usual controls in the output circuit. rate pivots but in practice they are Preferably According to a further feature of this invenmounted on a single shaft. The potentiometers 0 tion, the tubes are provided with individual grid are a part of the Voltage dividing network 46 4o biasing controls ganged in such a way that the extending between the output conductors 41 and bias on the two tubes may be Varied simul- 48 of the rectifier I6 and the positive potentials4 taneously in opposite directions. With this cirof the arms 33, 34 are impressed on the cathodes cuit the beam of a cathode ray tube may be 23,24 so that the grids 2|, 22 are effectively biased 5 safely and quickly adjusted to any desired posinegatively with respect to the cathodes. As the 45 tion on the screen of the tube. potentiometers are rotated clockwise the bias on 'Ihese and other features of the invention will grid 2l is decreased and the bias on grid 22 is be more clearly understood from the following correspondingly increased thereby increasing and detailed description and the accompanying drawdecreasing the plate currents of the tubes I4 and ing illustrating one embodiment of the invention l5, respectively. Similarly a contra-clockwise 5o 3,5 applied to Cathode ray Oscilloscopes, adjustment Will increase the plate Current Of the The cathode ray tube I is of a well-known type tube I5. These variations in the plate currents having a filament 2 for heating the cathode 3, a flowing through the resistors 21, 28 and 29, 30, control grid 4 and accelerator anodes 5 and 8, respectively will produce corresponding variaall of which are energized by a rectifier 6 opertions in the relative potentials of the plates I0, I0 55 and the position of the beam between the plates will vary in the same manner as if the potential differences were produced in the usual manner by controls in the high potential side of plate circuits.

The potentiometers and 36 may be used in a similar manner to vary the plate, currents of the tubes 31 and 38 and thereby control the lateral position of the electron beam between the plates 9, 9. These two potentiometer units therefore provide a safe and convenient means of centering the beam or of moving it to any desired position on the screen I I.

With the novel input circuit shown theseV oscilloscope ampliers. may be used in a number or" ways. When observing recurrent phenomena from an unbalanced source, terminals 39 and 40 of the vertical amplifier I2 (or terminals 4I and 5.2 of the horizontal amplifier I3) may be used. When amplifier I2 is so used potentiometer I1 is turned to some intermediate position according to the amplification required and since contact I8 is closed, the potential variations across the resistor 28 in the output of the tube I4 are impressed on the grid 22 of the tube I5. By a proper choice of the value of the resistor 28 the tubes I4 and I5 will therefore function as a balanced push-pull amplifier in the output circuit. When it is desired to observe the wave shape of the recurrent potential, the horizontal amplifier i3 may be driven by a relaxation oscillator or multiibrator to provide the necessary sweep circuit potential and this potential may be synchronized with the potential under observation by controlling the sweep circuit in the usual manner by a potential derived from the signal circuit such as that existing across the resistor 29.

When the phenomena are derived from a balanced source the potentiometer I is moved to its eXtreme clockwise position to open the` contact i8, input terminals 39 and 43 are used, and the ampliiier functions as a conventional push-pull circuit which may be used with or without a sweep circuit voltage as desired.

Since both the input and output circuits `are resistance coupled, the amplier will have a flat characteristic over a wide frequency band and even direct current (zero frequency) measurements may be made by using the terminals 39 and 43. A direct current potential applied to these terminals will change the relative potentials of the grids 2| and 22 and thereby deect the electron beam in the vertical plane in a manner similar to that already explained in connection with the use of the `ganged potentiometers 25 and 26.

While the invention has been described with reference to a particular application, it will be understood that it is capable of a variety of uses and that it may be modified in various ways within the scope of the following claims.

What is claimed is:

1. An amplifier comprising two vacuum tubes having input and output circuits connected in push-pull relation, a terminal connected to the input circuit of one of the tubes for unbalanced signal sources, a second terminal connected to the input circuit of the other tube for balanced signalsources only, means for deriving from the output of the one tube when operating from an unbalanced source a potential equal to the control potential at the input of said one tube, a feedback path for impressing the derived potential on the input of the other tube in opposed relation to the control potential in the input of said one tube, and means for opening the feedback path to condition the circuits for amplifying signals from a balanced source.

2. The combination with push-pull amplifier comprising two vacuum tubes having input and output circuits each including portions individual to the tubes and a grounded portion common to the tubes, of a feedback path from the output of one of the tubes to the input of the other tube, a switch in said path, and means for varying the impedance of the portion of the input circuit individual to said one tube and for operating the SWCh.

3. A push-pull ampliiier comprising two vacuum tubes having input and output circuits, an impedance across the input of each of the tubes, a feedback path from the output of one tube to the input of the other, and means for varying one of the impedances and for opening and closing the feedback path.

NATHANIEL C. NORMAN. 

